Retirees across the country are flocking to state parks, national wildlife refuges, and sanctuaries to lead bird watching tours, clear trails, and work in recreation centers (where one even makes cinnamon rolls), playing a crucial role in keeping the preserved places in top shape for visitors.

In return for a free place to pop their tents or park their RVs (and plug them in), “an itinerant, footloose army of available and willing retirees in their 60s and 70s is marching through the American outback, looking to stretch retirement dollars by volunteering to work in parks,” reports The New York Times.

The work that they’re doing is allowing some parks to keep their operations up and running. The flailing economy is forcing officials to cut staff and forgo non-essential obligations, like cleaning trash from trails, a task that’s important for wildlife and one that volunteers happily undertake.

The need for volunteers is so great that park administrators at the South Texas Refuge Complex earmark 65 campsites for them now, says Nancy Brown, the volunteer coordinator there. Ten years ago, they only set aside three.

“In some places, the retired volunteers are about the only staff members left,” according to the story. “’We did a state park in Arizona this year that had laid off so many people, we basically ran it,’ said Carolyn Miller, 71, a former small-business owner from Colorado who has work-camped from Alaska to Maine with her husband, Warren, 73.”

Without the volunteer corps, opportunities for a nature-hungry public would be even fewer than they are now, but that doesn’t seem to be what motivates the retirees. The reasons why the estimated 80,000 volunteers find their way to the parks are as diverse as the people themselves. Some, like retired biologist Wendy Forster, are pursuing a dream they shared with a departed spouse, while others just have a love of the outdoors—and now the time to spend in it.